Add test for block template name validation with underscores

[Sukhendu2002]

Trac ticket: https://core.trac.wordpress.org/ticket/62523

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[github-actions]

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[github-actions]

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[felixarntz]

@Sukhendu2002 Thank you for the PR! The test looks good, however instead of creating a new test class for it, it would be better to use the existing class for that purpose.

[Sukhendu2002]

Hey @felixarntz, Thanks for the review! I have moved the test to the existing test file. Take a look when you get a chance. Thanks!

[felixarntz]

@Sukhendu2002 Thank you for the updates, this looks great. Just one last point of feedback, then this should be good to commit.

[felixarntz]

Thanks @Sukhendu2002, LGTM!

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 59742
GitHub commit: 0dea78f

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.